Method and apparatus for preventing explosions in electrical apparatus



July 6, 1926. 1,591,163

T. T. GREENWOOD METHOD AND APPARATUS FOR PREVENTING EXPLOSIONS IN ELECTRICAL APPARATUS Filed April 29 1924 Patented July 6, 1926.

UNITED STATES 1,591,163 PATENT OFFICE.

TALMA T. GREENWOOD, OF EAST TEMPLETON, MASSACHUSETTS, ASSIGNOB, BY MESNE ASSIGNMENTS, TO CONDIT ELECTRICAL MANUFACTURING CORPORATION, 01? BOS- TON, MASSACHUSETTS, A CORPORATION MASSACHUSETTS.

METHOD AND APPARTUS FOR, PREVENTING EXPLOSIONS m ELECTRICAL;

' APPARATUS.

Application filed April-29, 1924. Serial No. 709,874.

This invention relates to electric switches wherein the circuit-interrupting arc is drawn in an arc-quenching fluid capable of forming gases and vapors which are explosive when mixed in suitable proportions with air; or other electrical apparatus containing a vaporizable combustible fluid; and has for' its object a method and apparatus for maintaining so great a proportion of the gases and vapors of the arc-quenching or insulatingfluidwith air that the mixture cannot explode.

The idea of maintaining the combustible content of the gaseous mixture too rich for the mixture to explode is also disclosed in my co-pending application Serial No. 67 5,- 949, filed November 20, 1923.

The figure represents diagrammatically an electric switch embodying the invention.

, As here shown the electric switch includes a casing 10 which may or may not be completely air tight. Said casing is adapted to contain the arc-quenching fluid, as oil, to some level 11, whereby to provide an expansion space 12 above the fluid level. Stationary switch members 13 extend into the oil and a bridging member 14 cooperates with said stationary switch members to control the current through the switch, The circuit-interrupting arc is drawn between the.

bridging member and the. stationary switch members.

Ordinarily fluid vapors and gases collect in the expansion space 12 and mix with the air contained therein to form an explosive mixture. 4

In accordance with this invention I provide a method and means for maintaining the mixture in the gas expansion space so rich in fluid vapors and gases that it can not explode. To this end I may arrange a conduit 15 in communication, at 16, with the fluid in the switch below the fluid level, and, at 17, with the ex ansion space 12 above the fluid level, where y fluid may stand in said conduit to the same level as in the switch casing. An electric heating element 18 is arranged in said conduit 15, mainly below the fluid level. Said heatin element may be supplied with current rom any suitable source as the current transformer 19 disposed in inductive relation to a stationary switch member 13, Said heating element 18 is adapted to boil the fluid in the conduit 15 and generate fluid vapor which is adapted approximately completely to fill the ex ansion space 12 and displace the air'contamed therein, which air may escape from the switch through suitable leakage paths or through the loaded check valve 20. Preferably fluid vapor is generated continually or while current is passing through the switch and the pressure of the fluid vapor in theyexpansion space is preferably about or slightly in excess of atmospheric pressure, whereb to prevent entrance of atmospheric air. T e capacity of the heating element 18 may be such as to maintain the pre-determined pressure regardless of the condensing effect of the cool walls of the switch casing.

Excess vapor pressure, as that generated upon circuit interruption may be relieved by the loaded check valve 20 which valve, preferably, is arranged to close when the pressure within the switch is approximately that of the atmosphere.

A fluid gage 22 may serve to indicate the fluid level within the casing and fluid may be added to the casing through said gage to compensate for fluid lost through vapor leakage.

B13; generatmg fluid vapor independently of t e switch or other electrical apparatus is not.

impaired,

he construction may be otherwise modified without departing from the spirit of the invention. s

I claim:

1. The method of preventing explosions in the casings, of electrical apparatus containing a fluid, the va or of which is explosive when mixed wit air, which method consists in generating vapor from the fluid in such quantities as to maintain the fluid vapor in the casin in such a large proportion of the total mixture content of the easing that the mixture cannot explode.

2. The method of preventing explosions in the casings of electrical apparatus con taining a fluid, the vapor of which is explosive when mixed with air, which method consists in heating a portlon of the fluid,

and generating vapor from the heated fluid in such quantities as to maintain the fluid vapor in the casing in such a large proportion of the total mixture content of the casing that the mixture cannot explode.

3. The method oi -preventing explosions in the casings of electrical apparatus containing a fluid, the vapor of which is explosive when mixed with air, which method consists in heating a portion of the fluid out of heat-transmitting relation'with the main bod the heated fluid in such quantities as to maintain the fluid vapor in the casing in such a large proportion of the'total mixture content of the casing that the mixture cannot explode.

4. The combination of an enclosing casing containing a vaporizable fluid, the vapor r which is explosive when mixed with air 1n suitable proportions, and an. expansion space above the fluid adapted-to contain air, electrical apparatus contained in the fluid, and means to generate vapor oi the'fluid to fill the ex ansion space to an extent to exclude deleterious quantities of air.

5. The combination of an enclosing casing containing a vaporized fluid, the vapor of which is explosive when mixed with air in suitable proportions, and an expansion space above the fluid adapted to contain air,-and means to heat the fluid locally and generate vapor ofthe' fluid to occupy the expansion space in a proportion so great that it is not explosive with the air therein.

6. The combination of an enclosing casing containing a vaporized fluid, the vapor of which is explosive when mixed with air in suitable proportions, and an expansion space above the fluid adapted to contain air, electrical apparatus contained in the fluid, and means to heat the fluid locally and generate vapor of the fluid to occupy substantially the entire volume of the expansion space and exclude other vapors or gases.

7. The combination of an enclosing casing containing a vaporizable fluid, the vapor of which is explosive when mixed with air in suitable proportions, and an expansion space above the fluid adapted to contain air, electrical apparatus contained in the fluid, means to heat a portion of the fluid external of the casing and generate vapor, and means to conduct the fluid vapor into the casing.

8, The combination of an enclosing casing containing a vaporizable fluid, the vapor of which is explosive when mixed with air in suitable proportions, and an expansion space above the fluid adaptedto contain air, electricalfapparatus contained in the fluid, and means to heat a portion of the fluid free from heat-imparting relation with the fluid body and liberate the vapor into-the expansion space.

9. The combination of an enclosing casing of fluid and generating vapor i'rom containing a vaporized fluid, the vapor or which is explosive when mixed with air in suitable proportions, and an expansion space above the fluid adapted to contain air, electrical apparatus contained in the fluid, and means to heat a portion of the fluid by the current traversing said electrical apparatus and liberate the vapor into the expansion space.

10. The combination of an enclosing casing containing a vaporizable fluid, the vapor of which is explosive when mixed with air in suitable proportions, and in expansion space above the fluid adapted to contain air, electrical apparatus contained in the fluid, a conduit disposed externally of the casing and having a fluid inlet in communication with the casing below the fluid level therein and having a vapor outlet in communication with the expansion space of the casing, and means to vaporize the fluid in said conduit.

11. The combination of an enclosing casing containing a vaporizing fluid, the vapor of which is explosive when mixed with air in suitable proportions, and an expansion space above the fluid adapted to contain air, electrical apparatus contained in the fluid, a conduit disposed externally of the casing and having a fluid inlet in communication with the casing below the fluid level therein and having a vapor outlet in communication with the expansion space of the casing, and a continually-operative electrical heating element arranged to vaporize the fluid in said conduit. 7

12. An electric switch comprising an enclosing casing adapted to contain a vaporizable arc-quenchin fluid and an expansion space above the flui stationary and movable switch members immersed in the fluid, an external conduit having a fluid inlet in communication with the interior of the casing below the fluid level therein and having a vapor outlet in communication with the ex' pansion space of the casing, and means to vaporize the fluid in said conduit.

13. An electric switch comprising an enclosing casing adapted to contain a vaporizable arc-quenching fluid and an expansion space above the fluid, stationary and movable switch members immersed in the fluid, an external conduit having a fluid inlet in communication with the interior of the casing below the fluid level therein and having a vapor outlet in communication with the ex; pansion space of the casing, and means to maintain va or of the fluid in said expansion space inclu ing an electrical heatin element arranged to vaporize the fluid in said conduit.

14. An electric switch comprising an enclosing casing adapted to contain a vaporizable arc-quenchi fluid and an expansion space above the fluid, stationary and movable switch members immersed in the fluid, an

external conduit having a fluid inlet in communication with the interior of the casing below the fluid level therein and having a vapor outlet in communication with the exduit, and a current transformer arranged in inductive relation with a switch member and connected with said electrical heating element.

15. An electric switch comprising an enclosing casing adapted to contain a vaporizable arc-quenchin fluid and an expansion space above the fluld, stationary and movable switch members immersed in'the fluid, an external conduit having a fluid inlet in communication with the interior of the casing 20 below the fluid level therein and having a vapor outlet in commuiiication with the expansion space of the casing, a d means to maintain vapor of the fluid in sai expansion space including an electrical heating element energized by the current traversing the switch arranged to vaporize the fluid in said 'conduit. arranged to vaporize the fluid in said con- 1c. The combination of a fluid containing receptacle, electrical apparatus contained in the'receptacle, a conduit disposed externally of the receptacle having upper and lower openings both arranged in communication with the interior of said receptacle respectively above and below the fluid level therein, and an electrical heating apparatus arranged in thermal relation with said conduit. I

In testimony whereof, I have signed my name to this specification.

TALMA T. GREENWOOD 

